RF Basics
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RF Basics
15/11/2013
Basic Terminology 1/2
• dBm – is a measure of RF Power referred to 1 mW (0 dBm)
• 10mW(10dBm), 500 mW (27dBm)
• PER – Packet Error Rate [%] – percentage of the packets not
successfully received over a period of time
• Used to measure the RF transceiver performance
• BER – Bit Error Rate [%] - percentage of the Bits not successfully
received over a period of time
• Used to measure the RF transceiver performance
• Sensitivity (RX) – it is the lowest input power of the receiver
acceptable to receive packets with 1% PER
• Blocking (RX) – The receiver ability to work in the presence of a
interfering RF signal in a frequency band relatively close to the signal
of interest
15/11/2013
Basic Terminology 2/2
• Dynamic range - the maximum received power variation at the
receiver input pins which result in a correct demodulated signal
• Adjacent Channels – channel(s) closest to the active signal channel
• Alternate Channel – second next channel(s) to the active signal
channel
• Payload – application data
• Modulation – superimposing algorithm of a low frequency signal
(payload) onto a high frequency signal (Carrier)
• ASK, OOK, FSK, GFSK, GMSK
15/11/2013
RF system
• Radio IC
Antenna
• Transmitter (only TX)
Radio IC
• Receiver (only RX)
Balun
• Transceiver (both TX & RX)
Match
Filter
Range
extender
Antenna
switch
• SoC (Transceiver + MCU)
Crystal
oscillator
Control
• Crystal
• Clocks the Radio IC crystal oscillator which generates the reference frequency for the RF synthesizer
• Balun
• converts balanced (differential) signal to unbalanced (single-ended) signal and the vice versa.
• Matching network
• whenever a source of power with a fixed output impedance such as a radio transmitter operates into a load, the
maximum possible power is delivered to the load when the impedance of the load is equal to the complex
conjugate of the impedance of the source
• Filter
• attenuates out of band signals
• Antenna switching
• Either can be used to switch from antenna to antenna
with a better RSSI value, or is switching the antenna either
to the RX to TX chain between the antenna and the radio IC
• Range Extender
• can be used to increase the radiated output power
• Antenna
• converts electric power into radio waves
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Complete RF communication environment
• Signal encoder / decoder
• converts information from one format or code to another, for the purposes of standardization,
speed, security or saving space by shrinking size (e.g. Manchester), decoder does the opposite
• Modulator
• process of varying one or more properties (amplitude, frequency, ..) of a high-frequency periodic
waveform, called the carrier wave, with a modulating signal which typically contains information
to be transmitted (Application Data)
• Communication channel
• is the physical transmission medium as a wire or, as in our case, a radio channel
• Demodulator / Detector
• Recovers the information content from the modulated carrier wave
Carrier wave
Application
Data
Signal
Encoder
Modulator
Communication
Channel (Air)
Transmitter
Demodulator
Detector
Signal
Decoder
Receiver
Carrier wave
Application
Data
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Digital Amplitude modulation methods
• ASK (Amplitude Shift Keying)
• The amplitude of an analog carrier signal varies in
accordance with the digital bit stream
• The amplitude of the carrier is set to a max level
when a 1 is sent and a min level when a 0 is sent
• Simple, duty cycling, lower transmit current
• Susceptible to noise, wide spectrum
• OOK (ON OFF Keying)
• It is the simplest form of ASK
• It represents digital data as the presence or absence
of a carrier
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Digital frequency modulation method (1/2)
• FSK
• The digital information is transmitted through
discrete frequency changes of a carrier
• Less susceptible to noise
• Theoretically it requires larger bandwidth than
ASK
• 2-FSK (Two level or binary FSK)
• A pair of discrete frequencies is used to
transmit 1/0
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Digital frequency modulation method (2/2)
• GFSK (Gaussian FSK)
• A Gaussian filter smoothes baseband data (1/0) to
make the pulse smoother
• It has better spectral width than 2-FSK
• MSK and GMSK
• MSK (Minimum Shift Keying)
• Is a type of continuous-phase frequency-shift keying
(CP-FSK)
• Is implemented as a fast frequency-shift keying (FFSK)
• The results is a constant-modulus signal => reduces
problems caused by distortion
• GMSK (Gaussian Minimum Shift Keying)
• A Gaussian filter is applied to smooth the incoming
digital data
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